This invention relates to a stereo X-ray fluorography apparatus for performing a stereo-fluorographic examination through viewing a subject by means of emission of X-rays alternately from right and left focal points of a stereo X-ray tube.
For performing a conventional X-ray diagnostic examination of the circulatory system, such as an angiographic examination of the brain, the heart and abdomen, an X-ray diagnostic apparatus is currently employed which can rapidly perform separate direct and indirect X-ray examinations.
In order to further enhance the diagnostic capacity in the case of angio-cardiography and coronary artery photography, considerable effort has been made to three-dimensionally examine the intricate spatial distribution of the blood vessels, by means of cinematic X-ray photography performed either in a plurality of directions or simply in two directions (using two X-ray tubes)
FIG. 1 shows a conventional X-ray fluorography apparatus for stereo-fluorographically examining a subject by means of exposure of X-rays alternately from two focal points of a stereo X-ray tube. FIG. 2 shows a signal waveform diagram.
Stereo X-ray tube 1 has two focal points located at a predetermined interval apart from each other and from which X-rays are emitted in alternate fashion. At the time of fluorography, a stereo X-ray image, a conventional continuous X-ray is not emitted, but a pulse-like X-ray, which is used in X-ray photography, is emitted alternately from the two focal points of the stereo X-ray tube, so that the subject may be alternately irradiated with X-rays from the right and left focal points. The emission of the X-rays from X-ray tube 1 is controlled by X-ray controller 18 which is made up of stereo X-ray tube control unit 2, high voltage generator 3, and X-ray control unit 4. The X-ray irradiation condition is automatically controlled so as to obtain optimal brightness. A high voltage is delivered from high voltage generator 3, through stereo X-ray tube control unit 3, atternately to right and left focal points of X-ray tube 1. The application of the high voltage and alternate emission of the X-rays from the right and left focal points, as described above, are controlled by an X-ray exposure trigger signal g. In FIG. 2, L1, R1, . . . show first X-ray exposure trigger signals from the left and right focal points, . . . , respectively.
The X-ray emitted from X-ray tube 1 passes through subject 5 and is supplied to image intensifier 6 where it is converted to a visible light image (fluorographic image). The fluorographic image is supplied to TV camera 8 through optical distributor 7 equipped with an image formation lens. With cinecamera 13 attached to optical distributor 7, stereo-cinephotographs can be taken through a predetermined operation of optical distributor 7. Fluorography unit 19 is made up of image intensifier 6, optical distributor 7, TV camera 8, and cinecamera 13.
TV camera control unit 9 is connected to TV camera 8 from which it is supplied with a video signal f, to allow the observation of the X-ray fluorographic image. Control unit 9 supplies a signal in synchronism with a vertical synchronizing signal of the video signal f to X-ray control unit 4, which in turn supplies the X-ray exposure trigger signal g to stereo X-ray tube control unit 2.
Control device 4 conveys a signal in synchronism with the vertical synchronizing signal to stereo glass control unit 11, which, on the basis of this signal, in turn drives a pair of glasses 12. The respective lenses of glasses 12 are each made up of a liquid crystal shutter to which a polarizing sheet is attached. Therefore, the transmittance of the lens is electrically varied either to allow the passage or block the passage of incoming light. Unit 11 supplies complementary transmitting and non-transmitting control signals h, i to left- and right-eye lenses, in synchronism with every TV field, so that the images of X-rays emitted from the right and left focal points of X-ray tube 1, after their transmittance through the subject, are observed only through the right- and left-eye lenses, respectively.
In this way, the synchronization of the X-ray irradiation with the TV field and stereo glasses 12 is achieved, so that X-ray irradiation is performed at a rate of 60 times per second, with the alternate switching of the left- and right-eye lenses being performed at a cycle of 1/60 (second). In this way, it is possible to observe the visualized image as a stereo image through the pair of glasses.
In practice, because of the image persistence phenomenon which occurs in the image pickup tube of a TV camera, the image emitted from the focal point on one side of the stereo X-ray tube persists faintly while a new image appears in the next TV field, with the result that it appears overlapping this image, which is emitted from the focal point on the other side of the stereo X-ray tube. Consequently, it is difficult for the operator to view the image as a stereo image. In addition, flickering of the main image is liable to occur, due to the alternate switching of the images emitted from the left and right focal points of the stereo X-ray tube.